<template>
 <ul class="list">
   <li class="item"
   v-for="item of letters"
   :key="item" :ref="item"
   @click="hadelClick"
   @touchstart="handelTouchStart"
   @touchmove="handelTouchMove"
   @touchend="handelTouchEnd">
     {{item}}
   </li>
 </ul>
</template>
<script>
export default {
  name: 'CityAlphabet',
  data () {
    return {
      touchStatus: false,
      startY:0,
      timer: null
    }
  },
  updated () {
     this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for(let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  methods: {
    hadelClick(e){
      this.$emit('change',e.target.innerText)
    },
    handelTouchStart () {
      this.touchStatus=true
    },
    handelTouchMove (e) {
      if(this.touchStatus) {
        if (this.timer){
          clearTimeout(this.timer)
        }
        this.timer=setTimeout(() => {
          const touchY =e.touches[0].clientY - 79
        const index = Math.floor((touchY-this.startY)/20)
        if(index >= 0 && index < this.letters.length){
          this.$emit('change',this.letters[index])
        }
      },16)
    }
   },
    handelTouchEnd () {
      this.touchStatus=false
    }
  },
  props: {
    cities:Object
  }
}
</script>
<style lang="stylus" scoped>
  @import '~@/assets/styles/veribles.styl'
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    .item
      line-height .4rem
      text-align center
      color $bgCOlor

</style>
